This invention relates to the field of display systems and more particularly to passive display systems that have internal supplemental lighting.
In the design of portable electronics equipment, such as selective call personal paging receivers, portable two way radios, pocket calculators, and watches, there has been a trend to make such devices smaller in size and to crowd more features into a given package size. The result is that there is less space on the package to position controls such as switches. To compensate for the lack of control space, some functions that were previously handled by separate controls may often be combined.
In a device that utilizes a passive display with internal supplemental lighting, the functions of transferring the message to the display and activating the internal supplemental lighting source can be combined and controlled by a common "read" switch. Combining these two functions, however, results in increased battery drain, a problem that may already be complicated by the fact that a reduction in the package size necessitates a reduction in battery size and capacity. This increase in battery drain may often not be necessary, however, because ambient light conditions may be sufficiently strong such that internal supplemental lighting is not required. This problem can be overcome by providing the device with a means to sense the ambient light intensity and if it is below a threshold level, then, and only then, can the internal supplemental light source be activated by the read switch.